The invention relates to a television circuit for a picture flicker correction, provided with a first and a second delay device coupled to an input terminal of the television circuit, which delay devices each have a delay time substantially corresponding to a field period, inputs of a first and a second adding circuit being respectively connected in parallel with the first and the second delay devices, the outputs of the first and second adding circuits being coupled to respective inputs of a first switch-over device which has a switching input for a switching signal which controls the switching of the switch-over device at each field period, the output of the switch-over device being coupled to the output terminal of the television circuit.
A circuit of this kind is known from U.S. Pat. No. 4,090,218, in particular from FIG. 7a where it is described that in a video disc display system which includes the feature of stop-motion, or a still television picture, produced by repeated display of the information of two fields, such display normally gives rise to a flicker phenomenon which does not occur with continuous display. This is due to the occurrence of motion which takes place in the scene televised in the interval between the pick-up instants of the two fields. Repeated display of the two fields including the information shift between the two partial pictures, which shift is due to the motion in the scene, gives rise to the flicker phenomenon, which occurs at frame frequency.
To effect flicker correction, it is proposed, with the aid of the delay devices, the adding circuits and the switch-over device, to form combinations of video information divided into discrete groups which each comprise two associated field periods and to record these preformed combinations on the video disc. The repeated display of groups of two associated fields eliminates flicker upon display of the stop-motion or still picture.
The problem described is equally present in television displays using field and line frequency doubling. Here, a sequence of television fields ABCD etc., in the four field periods given as an example, is displayed in the sequence AABBCCDD or in the sequence ABABCDCD. Both methods AABB and ABAB have the advantage that the field frequency of 50 or 60 Hz is increased to 100 or 120 Hz, as the result of which field frequency flicker also occurs at the doubled frequency and is no longer perceptible. Here the method ABAB has the further advantage that a 25 or 30 Hz line flicker is converted into a 50 or 60 Hz line flicker, which is much less troublesome. A drawback of the ABAB method, however, is the occurrence of the troublesome flicker phenomenon, as described, when playing the video disc with the stop-motion possibility.
The U.S. Pat. No. 4,090,218 describes that, irrespective of the picture content upon pick-up and display, the video signal combinations continue to be produced even where, owing to the absence of a local change in video information, often caused by movement in the picture, this is not necessary. Further a movement detector has been developed which makes accurate movement detection possible.